1. Field of the Invention
The present invention relates to a control device for an air-conditioner, and in particular to a control device for an automotive heat-pump type air conditioner which can be shifted between heating and cooling modes through a valve, for example an electromagnetic valve, a three-way valve, a four-way valve or a check valve.
2. Description of Related Art
A typical heat-pump type air-conditioner or climate control system is described hereinafter. The heat-pump type air-conditioner generally includes a first heat-exchanger disposed within an air-conditioning duct, a second heat-exchanger disposed outside the air-conditioning duct, refrigerant expanding means such as an orifice or an expansion valve which are disposed between the two heat exchangers, a four-way valve for changing a flow direction of refrigerant in the two heat-exchangers, a compressor for compressing the refrigerant, and a receiver tank. The air-conditioner thus constructed is switched from a cooling mode into a heating mode or vice versa by shifting the four-way valve to change the flow direction of the refrigerant flowing in the first and second heat exchangers. Such a heat-pump type air-conditioner has an advantage in that both the heating and cooling modes can be accomplished by using one heat-exchanger, the heat exchanger functioning as a condenser for heating the air passing therethrough in the heating mode and as an evaporator for cooling the air passing therethrough in the cooling mode.
However, it is impossible in this type of air-conditioner, and also in other conventional air-conditioners such as those which use a three-way valve and/or an electromagnetic valve with no reversal of the refrigerant flow, as described in Japanese U.M. publication Nos. 50-21710 and 61-101020, to consecutively shift the heating mode into the cooling mode and vice versa while varying the temperature in a linear manner, and thus such air-conditioners must have two separate switches, i.e. a shift switch for shifting the air-conditioner between the heating mode and the cooling mode and a temperature adjustment switch for controlling the heating or cooling capacity of the heat exchanger, that is, for increasing and decreasing a rotational number or speed of the compressor.
Therefore, a driver or passenger must operate two switches in order to implement a particular temperature control request, which increases the difficulty of operating the air-conditioner, impeding safe operation of the vehicle.